Low-temperature plasma coupled high-activity and low-cost zero-valent iron synthesis ammonia process

Abstract

This invention discloses a low-temperature plasma-coupled, highly active, low-cost process for synthesizing ammonia using zero-valent iron, belonging to the field of ammonia synthesis technology. The process comprises: using a plasma reactor with hydrogen as a reducing agent to induce a plasma hydrogen reduction reaction in a Fe2O3 source to synthesize zero-valent iron; and using the synthesized zero-valent iron as a catalyst to induce a plasma ammonia synthesis reaction between H2 and N2 to produce ammonia. The plasma ammonia synthesis reaction is carried out at atmospheric pressure and a reaction temperature of 220-300℃. This invention, driven by low-temperature plasma, pioneers a cross-industry co-production process of "iron ore reduction-ammonia synthesis" in a single system. Specifically, it directly uses zero-valent iron obtained from the efficient reduction of iron ore by hydrogen-based plasma as a catalyst for low-temperature plasma ammonia synthesis. The overall process is simple, the synthesis conditions are mild, and the catalyst cost is low.

Description

Technical Field

[0001] This invention belongs to the field of ammonia synthesis technology, and more specifically, relates to a low-temperature plasma-coupled, highly active, low-cost zero-valent iron ammonia synthesis process. Background Technology

[0002] In the first half of the 20th century, Haber and Bosch developed the Haber-Bosch process, enabling the industrial synthesis of ammonia and making humanity highly dependent on ammonia products. Ammonia has traditionally been used primarily in fertilizers, military raw materials, and pesticides; recent research has expanded to areas such as refrigeration, fermentation, and energy carriers. Due to its high hydrogen content, ammonia and its derivatives, such as ammonium bromide, are considered among the most efficient and economical hydrogen carriers. Ammonia has a heat of combustion of approximately 22 MJ / kg, a relatively low calorific value comparable to diesel fuel; its high boiling point also makes it an ideal material for indirect hydrogen storage. Furthermore, the complete combustion of ammonia is a sustainable process that does not emit any greenhouse gases. Therefore, ammonia or ammonium bromide has also been introduced into petroleum-based fuels for use in vehicle engines to improve emissions cleanliness.

[0003] The Haber-Bosch process can provide over 130 million tons of ammonia annually, supporting approximately 40% of the global population. However, it consumes about 2% of global energy annually and requires high-temperature, high-pressure conditions, resulting in high investment and operating costs and hindering miniaturization and decarbonization. Therefore, current research is gradually shifting towards exploring synthesis methods driven by renewable electricity under milder conditions. The advantages of non-thermal plasma in ammonia synthesis lie primarily in its ability to directly excite nitrogen molecules using high-energy electrons, potentially opening up more energy-efficient reaction pathways than traditional thermocatalysis (such as hydrogen-assisted dissociation of N≡N). Its core advantage lies in bypassing the stringent high-temperature, high-pressure dependence of the traditional Haber-Bosch process, paving a new path for sustainable, distributed ammonia production.

[0004] A search revealed numerous patents published regarding plasma ammonia synthesis processes and catalysts used in ammonia synthesis.

[0005] For example, Chinese invention patent CN 118179574 A discloses a supported metal catalyst coupled with porous materials for low-temperature plasma ammonia synthesis, its preparation method, and its application. This method first prepares a cerium oxide nanoisland support, then obtains a copper-iron alloy-cerium oxide nanoisland catalyst, which is then mixed with a mesoporous material and calcined to finally obtain the catalyst-coupled porous material. This material can significantly improve the efficiency of low-temperature plasma ammonia synthesis, with Cu4Fe1-CeO as the most suitable candidate. x Catalysts represented by SiO2 have extremely high catalytic activity and can stably produce NH3 at high power.

[0006] For example, Chinese invention patent CN 120905684 A discloses a low-temperature plasma-coupled electrocatalytic ammonia synthesis process, which mainly consists of three steps: First, air and water vapor react in a plasma reactor filled with a special catalyst to generate NO-containing... x The gas is then electrocatalyzed and reduced to ammonia-containing products. Finally, ammonia is efficiently separated and purified using an innovative photothermal separation module. The core of this process is a multi-level heterojunction gradient-doped carbon-coated catalyst. This catalyst, through gradient doping of boron and sulfur and surface loading of Au nanoparticles, synergistically enhances the reaction activity and stability, thereby achieving efficient and green ammonia synthesis under mild conditions.

[0007] Among them, Chinese patent CN 118179574 A focuses on developing highly efficient supported metal catalysts (such as Cu4Fe1-CeO). x While CN 120905684 A integrates plasma and electrocatalysis and introduces photothermal separation and purification, its core is still based on NO. (SiO2) to enhance the activity of plasma ammonia synthesis, but it remains limited to a single ammonia synthesis process; CN 120905684 A integrates plasma and electrocatalysis and introduces photothermal separation and purification, but its core is still based on NO. x The reduction-based ammonia synthesis route, involving the precious metal Au as a catalyst, is costly. Neither approach breaks the traditional model of separate production in the steel and chemical industries. In other words, current research focuses on a single reaction, resulting in a relatively singular form of energy utilization. While CN 120905684 A incorporates photothermal separation, the superposition of multiple energy conversion stages—plasma power generation, electrocatalysis, and photothermal processes—poses challenges to system complexity and overall energy efficiency. Furthermore, catalyst cost (especially those containing precious metals) and system complexity are potential economic obstacles to large-scale industrial applications. Summary of the Invention

[0008] To address the challenges of traditional ammonia synthesis processes, which require stringent high-temperature and high-pressure conditions, and plasma ammonia synthesis processes, which suffer from high catalyst preparation costs and / or high system complexity, hindering industrial application, this invention provides a low-temperature plasma-coupled, highly active, and low-cost zero-valent iron ammonia synthesis process. This invention pioneers a cross-industry co-production process of "iron ore reduction-ammonia synthesis" within a single system, driven by low-temperature plasma. Specifically, it directly uses zero-valent iron, obtained through the efficient reduction of iron ore (Fe2O3) using hydrogen-based plasma, as the catalyst for low-temperature plasma ammonia synthesis. The overall process is simple, the synthesis conditions are mild, and the catalyst cost is low, thus facilitating industrial application.

[0009] To achieve the above objectives, the technical solution provided by this invention is as follows:

[0010] This invention provides a low-temperature plasma-coupled, highly active, low-cost process for synthesizing ammonia from zero-valent iron, comprising: A plasma reactor was used with hydrogen as a reducing agent to induce a plasma hydrogen reduction reaction in the Fe2O3 source in order to synthesize zero-valent iron. Using the zero-valent iron synthesized above as a catalyst, H2 and N2 are subjected to a plasma synthesis reaction to prepare ammonia; wherein, the plasma synthesis reaction is carried out under normal pressure and the reaction temperature is 200~300℃.

[0011] Traditional ammonia synthesis processes suffer from demanding reaction conditions, requiring high temperatures and pressures. Existing plasma ammonia synthesis processes face core challenges such as high catalyst preparation costs and / or process separation, hindering industrial application. To address this, this application first uses an Fe2O3 source for plasma hydrogen reduction to synthesize zero-valent iron. This synthesized zero-valent iron is then used as a catalyst for the plasma ammonia synthesis reaction. This approach not only effectively ensures the efficiency and concentration of the plasma ammonia synthesis reaction but also significantly reduces catalyst costs. Furthermore, the overall process is simple and the reaction conditions are mild (lower reaction temperature; existing technologies typically require much higher temperatures, around 500°C).

[0012] Furthermore, the plasma hydrogen reduction reaction and the plasma ammonia synthesis reaction are carried out in the same plasma reactor.

[0013] Furthermore, after the plasma hydrogen reduction reaction is completed, the synthesized zero-valent iron is kept in the plasma reactor, and the temperature inside the reactor is reduced to the plasma ammonia synthesis reaction temperature range, so that it can continue to be used for plasma ammonia synthesis reaction.

[0014] Furthermore, it also includes: recovering hydrogen from the plasma hydrogen reduction reaction and continuing to use it as a raw material for the plasma ammonia synthesis reaction, thereby realizing the cascading and recycling of hydrogen within the process, and directly using the unreacted hydrogen in the reduction section as a raw material for ammonia synthesis, which greatly improves the overall utilization efficiency of hydrogen atoms.

[0015] Preferably, the Fe2O3 source is iron ore. Therefore, this invention pioneers a cross-industry co-production process of "iron ore reduction-ammonia synthesis" in a single system. Its fundamental breakthrough lies in the fact that the system uses highly active zero-valent iron synthesized in situ as the sole catalyst. This catalyst possesses extremely high catalytic activity, completely eliminating the need for precious metals and complex supports, achieving catalyst self-sufficiency and near-zero cost. Based on this, the process simultaneously completes the internal recycling of hydrogen and efficient ammonia synthesis (concentration up to 22,000 ppm) under mild conditions (atmospheric pressure, ≤300℃), thus providing a completely new technical path for deep decarbonization in the steel and chemical industries.

[0016] Furthermore, the method also includes: after the plasma ammonia synthesis reaction is completed, the zero-valent iron sample is subjected to low-oxygen treatment using a mixture of inert gas and oxygen, wherein the mass percentage of oxygen in the mixture is 1% to 4%. Low-oxygen treatment effectively prevents the oxidation of zero-valent iron, maintains its original properties, facilitates storage, and has low processing costs. For example, argon can be used as the inert gas.

[0017] Furthermore, the iron ore has a particle size of 0.1~3mm, more preferably 1~3mm. Optimizing the particle size of the iron ore raw material helps to further improve and ensure the metallization rate and reduction effect of the plasma hydrogen reduction reaction. However, when the iron ore particle size is too small (<0.1mm), there are more Fe3O4 phases after Fe2O3 reduction, resulting in a relatively poor reduction effect.

[0018] Furthermore, the plasma hydrogen reduction reaction is carried out at a temperature of 400-500°C for 1-2 hours.

[0019] Furthermore, the discharge portion of the plasma reactor is heated by a furnace, which facilitates the regulation of the temperature inside the reactor.

[0020] Preferably, during the plasma hydrogen reduction reaction, a mixture of hydrogen and argon is introduced into the reaction system, with a total flow rate of 1-2 L / min and a volume ratio of H2:Ar of 3:1-6:1.

[0021] The total flow rate of the mixed gas has a significant impact on the plasma hydrogen reduction effect. When the total flow rate of the mixed gas is too low, the plasma hydrogen reduction effect is poor, and there may even be cases where hydrogen is not reduced, thus affecting the ammonia synthesis effect. As the total flow rate of the mixed gas increases, the content of highly active zero-valent iron increases, thereby increasing the concentration of synthesized ammonia.

[0022] Preferably, the plasma input power is controlled to be 80~120 W. More preferably, the power supply for the plasma hydrogen reduction reaction is 80~90 W, and the power supply for the plasma ammonia synthesis reaction is 100~120 W, and even more preferably 110~120 W.

[0023] As the input power for ammonia synthesis increases, the electron density and energy of the plasma are enhanced, generating more highly active hydrogen atoms, ions, and excited-state species. These active hydrogen species can not only participate more effectively in the surface hydrogenation step, but also help maintain the reduced state of active sites on the catalyst surface (such as zero-valent iron), thereby promoting nitrogen activation and ammonia synthesis reactions. Therefore, the concentration of ammonia synthesis increases with increasing power.

[0024] More preferably, the total flow rate of the mixed gas in the plasma hydrogen reduction reaction is 1.5~2 L / min, and the power of the plasma ammonia synthesis reaction is 110~120 W. Under a higher reducing gas flow rate, the higher power further enhances the efficient dissociation and activation of hydrogen by the plasma, and works synergistically with the increased zero-valent iron active sites to form a stronger "active hydrogen-active site" coupling, thereby maximizing the concentration of synthesized ammonia.

[0025] Furthermore, the total flow rate of the H2 and N2 mixture in the plasma ammonia synthesis reaction is 45~60 ml / min, wherein the volume ratio of H2:N2 is 3:1.

[0026] Compared with the prior art, this application can achieve the following beneficial effects: (1) This invention provides a novel low-temperature plasma coupling process for synthesizing ammonia with high activity and low cost of zero-valent iron. In a single low-temperature plasma system, the two core reactions of “Fe2O3 reduction (preferably using iron ore directly)” and “ammonia synthesis”, which belong to different industrial fields, are coupled and completed. This realizes the direct co-production of high activity zero-valent iron and ammonia from iron ore, opening up a disruptive technology direction for cross-industry coupling between iron and steel and chemical industries.

[0027] (2) The plasma hydrogen reduction reaction and plasma ammonia synthesis reaction of the present invention can be carried out in the same plasma reactor. That is, a single process can simultaneously produce two high-value basic products: high-activity zero-valent iron (which can be used as a low-carbon metallurgical raw material, degraded in pharmaceutical wastewater, and used to prepare high-value-added chemicals and energy) and synthetic ammonia, reducing the energy consumption and equipment investment cost per unit product and enhancing the economic competitiveness of the overall process.

[0028] (3) Under mild conditions of normal pressure and medium to low temperature (≤500℃), the present invention simultaneously achieves efficient reduction of iron ore (metallization rate ≥99.9%) and high-concentration synthesis of ammonia (temperature 300℃). o At C, the outlet concentration reached as high as 22,000 ppm, thus proving the technical feasibility of bifunctional synergistic catalysis. Simultaneously, it achieved self-supply and high activity of the catalyst in the ammonia synthesis process, with the catalyst derived from highly active zero-valent iron generated on-site by the process itself. This completely eliminates the need for precious metals (such as Au) or complex composite catalysts (such as Cu-Fe-CeO). x It eliminates external dependence on gradient-doped carbon materials and significantly reduces material and catalyst costs: using inexpensive Fe2O3 as the sole raw material, catalysts are generated through internal process circulation, achieving "zero-cost" self-supply of catalysts and completely avoiding the high material costs brought about by precious metals and complex catalyst supports.

[0029] (4) The present invention provides a low-cost, zero-carbon and efficient ammonia synthesis method that achieves deep decarbonization from the source and helps achieve the "dual carbon" goal. The entire process is powered by low-temperature plasma driven by green electricity. The reaction process does not require carbon-based reducing agents and realizes internal hydrogen circulation. In principle, the co-production process of iron and ammonia is close to zero carbon emissions, providing a revolutionary solution for the green transformation of the two high-carbon industries of steel and chemical.

[0030] (5) The present invention provides a low-cost, zero-carbon and efficient method for synthesizing ammonia. It innovatively treats the sample after the reaction with low oxygen, which effectively prevents the Fe in the sample from being rapidly oxidized by air. Moreover, the method can avoid the oxidation of the sample for a long time and maintain its original performance, thereby providing a new way to avoid the oxidation of zero-valent iron and greatly reducing the cost of anti-oxidation measures. Attached Figure Description

[0031] Figure 1 The XRD patterns are of Fe2O3 samples of different particle sizes after plasma hydrogen reduction at a total gas flow rate of 0.4 L / min. Figure 2 The XRD patterns are of Fe2O3 samples of different particle sizes after plasma hydrogen reduction at a total gas flow rate of 2 L / min. Figure 3 XRD comparison images of samples after molecular hydrogen reduction and plasma hydrogen reduction of iron; Figure 4 H2-TPD test curves of samples after molecular hydrogen reduction and plasma hydrogen reduction of iron; Figure 5 EPR test curves of samples after molecular hydrogen reduction and plasma hydrogen reduction of iron; Figure 6 This is a schematic diagram of the experimental process of one embodiment of this application. Detailed Implementation

[0032] Addressing the shortcomings of existing ammonia synthesis processes, this application proposes and realizes for the first time a cross-industry coupling of low-temperature plasma-driven "ironmaking-ammonia synthesis," pioneering a new technical route for the simultaneous production of elemental iron and ammonia in a single process. Its core innovation lies in: (1) Material and cost advantages: The catalyst used in this process is directly derived from zero-valent iron generated in situ in the process itself. The preparation of zero-valent iron uses only inexpensive Fe2O3 as the only raw material. No precious metals (such as gold, platinum) or complex support materials (such as cerium oxide, gradient doped carbon materials) need to be introduced. While significantly reducing the cost of raw materials, it still has high catalytic activity.

[0033] Furthermore, under optimized plasma process conditions, highly efficient preparation of near-complete reduction of zero-valent iron can be achieved, with a metallization rate as high as 99.9%. This can continuously provide sufficient and highly active catalytic sites for the ammonia synthesis reaction, realizing self-supply and low cost of catalysts from the source.

[0034] (2) Disruptive process coupling: The hydrogen-based reduction of iron ore powder and the synthesis of ammonia are integrated into the same low-temperature plasma reactor, which can achieve "one reactor for two purposes". The highly active zero-valent iron generated in the reduction section is "produced and used immediately" as a catalyst for the synthesis of ammonia without the need for additional preparation; at the same time, the unused hydrogen in the reduction tail gas can be directly used as a raw material for the synthesis of ammonia, realizing "one iron for two purposes and one gas for two purposes", and completing the in-situ cascade of mass, energy and resources.

[0035] (3) Technological Breakthrough and Feasibility: Addressing the challenges of the plasma dual-function excitation mechanism (requiring simultaneous driving of iron ore reduction and ammonia synthesis) and the cross-scale mass-energy transfer within the reaction zone, this process successfully achieved efficient ammonia synthesis under ambient pressure and mild conditions (reduction zone ≤ 500℃, synthesis zone ≤ 300℃) using in-situ generated highly active zero-valent iron as a catalyst, with an outlet concentration as high as 22,000 ppm. This result verifies the feasibility of the core pathway of "reduced iron as catalyst," marking a technological breakthrough in synergistically achieving dual functions of reduction and catalysis in a single plasma system.

[0036] In other words, this application not only solves the efficiency and cost problems of synthetic ammonia, but also achieves a zero-carbon transformation from the source through the deep integration of steel and chemical industries, providing new technical guidance for the green revolution of high-carbon emission industries around the world.

[0037] To further understand the present invention, specific embodiments are now described in detail. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of this disclosure. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the embodiments of this disclosure for ease of explanation. However, it will be apparent that one or more embodiments may be practiced without these specific details. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concepts of this disclosure.

[0038] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. The terms “comprising,” “including,” etc., as used herein indicate the presence of the stated features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0039] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein are to be interpreted in a manner consistent with the context of this specification, and not in an idealized or overly rigid way.

[0040] Example 1 Combination Figure 6 As shown, the low-temperature plasma-coupled, highly active, low-cost zero-valent iron ammonia synthesis process of this embodiment includes: Step 1: Plasma hydrogen reduction of iron stage; 20g of high-purity Fe2O3 particles (with a particle size distribution of 1-3mm) were placed in a plasma reactor. A mixture of H2 and Ar gas (total gas flow rate of 2 L / min, H2:Ar volume ratio of 4:1) was introduced into the reactor, and a plasma hydrogen reduction reaction was carried out at 500℃ to synthesize zero-valent iron.

[0041] Specifically, this embodiment uses a CTP-2000K low-temperature plasma experimental power supply, with an output voltage of 0–30 kV, a frequency adjustable range of approximately 30%, a rated power of 500 W, and a center frequency selectable range of any point between 1 and 100 kHz. This power supply is specifically designed for plasma experiments and possesses high efficiency and stable performance. In this embodiment, the power input for the plasma hydrogen reduction of iron stage is controlled at 80 W, and the reduction time is 2 hours. In this embodiment, a VTL1200 tubular furnace is used to control the reaction temperature within the reactor.

[0042] A liquid chromatograph was connected to the reactor tail gas outlet to monitor the hydrogen concentration after plasma hydrogen reduction of iron online. The hydrogen utilization rate of plasma hydrogen reduction of iron was obtained by subtracting the hydrogen concentration after the reaction from the hydrogen concentration before the reaction and then dividing by the hydrogen concentration before the reaction. Subsequently, a gas collection tank was used to recover the tail gas after plasma hydrogen reduction (the tail gas produced by the plasma hydrogen reduction of iron reaction consists only of H2 and H2O, and the H2O is filtered before collection) for subsequent ammonia synthesis.

[0043] Step 2: Plasma synthesis of ammonia reaction stage; After the plasma hydrogen reduction of iron reaction is completed, the zero-valent iron catalyst is kept in the reactor for ammonia synthesis. The H2 recovered in step one is used as a gaseous feedstock, and an appropriate amount of N2 is added. The H2 and N2 are mixed by passing them through a gas mixing device, with the total flow rate of the H2 and N2 mixture set at 60 ml / min, and the H2:N2 volume ratio at 3:1. In the ammonia synthesis process, the plasma power input is controlled at 120 W, and the plasma reactor temperature is controlled at 300 °C. A liquid chromatograph is connected to the reactor tail end to detect the concentration of plasma-synthesized ammonia.

[0044] Step 3: Measures to prevent sample oxidation after reduction; After ammonia synthesis is complete, Ar is introduced into the reactor as a protective gas, and the reactor temperature is allowed to drop to 50°C. o After the temperature drops below a certain point, turn off Ar and introduce an Ar-O2 mixture (98% Ar and 2% O2) into the reactor for 1.5 hours at a total flow rate of 200 ml / min. -1 At this point, a protective layer forms on the surface of the reduced sample, which effectively prevents the sample from being oxidized by air and does not affect the metallization rate or performance of the sample.

[0045] Comparative Example 1 The main difference between this comparative example and Example 1 is that the total flow rate of the H2 and Ar mixed gas in the plasma hydrogen reduction iron stage in this comparative example is 0.4 L / min.

[0046] With the total flow rate of the mixed gas in the plasma hydrogen reduction stage of iron remaining constant at 0.4 L / min, the reduction effect of plasma hydrogen under different particle sizes was tested and analyzed. The total iron, metallic iron, and metallization rate of the reduced products are shown in Table 1. As can be seen from Table 1, the metallization rate of the plasma hydrogen-reduced samples gradually increases with the increase in Fe2O3 particle size, but the increase is not significant, and the metallization rate is generally low. Among them, the reduction effect of Fe2O3 particles <0.1 mm is the lowest, with a metallization rate of only 15.72%. The highest metallization rate of 19.19% is achieved within the Fe2O3 particle size range of 1-3 mm. Under these conditions, the iron content of the reduced samples is generally low.

[0047] Through XRD data (such as Figure 1 As shown in the figure, regardless of the particle size, the reduced sample contains Fe3O4 phase and even Fe2O3 phase. This further verifies that the plasma hydrogen reduction effect is poor under the condition of a total gas flow rate of 0.4 L / min, and there are even cases where hydrogen is not reduced.

[0048] Table 1 Comparison of hydrogen reduction effects of Fe2O3 plasma with different particle sizes at a total flow rate of 0.4 L / min for the H2 and Ar mixed gas mixture.

[0049] In addition, the concentration of synthesized ammonia was increased mainly due to the increase in the total flow rate of reducing gas and the increase in the content of highly active zero-valent iron.

[0050] Example 2 The main difference between this embodiment and Embodiment 1 is that the particle size distribution of Fe2O3 particles in this embodiment is 0.1-1 mm.

[0051] Comparative Example 2 The main difference between this comparative example and Example 1 is that the particle size of the Fe2O3 particles in this comparative example is <0.1 mm.

[0052] As shown in Table 2, when the total flow rate of the mixed gas in the plasma hydrogen reduction stage of iron was adjusted to 2 L / min, the metallization rate of the sample after plasma hydrogen reduction gradually increased with the increase of Fe2O3 particle size, and was significantly improved compared with the sample at 0.4 L / min. However, when the Fe2O3 particle size was small (<0.1 mm), the reduction effect was still poor, only 42.57%. When the Fe2O3 particle size was in the range of 1-3 mm, the metallization rate could reach the highest of 99.89%. Under this condition, the reduced sample was pure iron, achieving the optimal reduction effect.

[0053] Combination Figure 2 The XRD data shown indicates that a significant amount of Fe3O4 phase exists after the reduction of Fe2O3 particles smaller than 0.1 mm. However, as the Fe2O3 particles become larger, the Fe3O4 phase gradually decreases. In the 1-3 mm particle size range, only the Fe phase exists in the phase composition. This further proves that the Fe2O3 particles in this group have been completely reduced to zero-valent iron. Under these conditions, nearly 100% reduction of iron was successfully achieved.

[0054] Table 2 Comparison of hydrogen reduction effects of Fe2O3 plasma with different particle sizes at a total flow rate of 2 L / min for the H2 and Ar mixed gas.

[0055] Comparative Example 3 The main difference between this comparative example and Example 2 is that in the plasma hydrogen reduction iron stage, no plasma is applied in this comparative example, that is, only molecular hydrogen reduction is performed.

[0056] After reduction, the metallization rate and XRD of the reduced samples in Comparative Example 3 and Example 2 were compared and analyzed. In terms of activity, EPR and H2-TPD characterization were used to verify the oxygen vacancy concentration and H2 adsorption capacity of the samples after the reaction. The results showed that, under the same reduction conditions, the metallic iron content of the molecular hydrogen-reduced sample was 59.34%, and the metallization rate was only 66.15%; while the metallization rate of plasma hydrogen reduction was higher, reaching 90.47%.

[0057] And the XRD results show (as) Figure 3 Under molecular hydrogen reduction conditions, a large amount of Fe3O4 phase exists, while plasma reduction is mainly dominated by the Fe phase. Therefore, this indicates that plasma reduction conditions can achieve the best reduction effect for iron.

[0058] To further investigate the effects of the two reduction conditions on the activity of the samples, H2-TPD tests were performed on the corresponding samples, and the results are as follows: Figure 4 As shown, the desorption peak appearing at approximately 140°C is attributed to the desorption of hydrogen from physical adsorption or weak chemisorption. There is no significant difference in peak shape between the two conditions in this low-temperature region, except that the plasma-reduced sample shows a slightly higher desorption amount. The high-temperature desorption peak corresponds to the desorption of strongly adsorbed hydrogen: the high-temperature desorption peak of the plasma-reduced hydrogen sample is located at 449°C, while the corresponding peak of the molecular hydrogen-reduced sample is located at 404°C. Clearly, the plasma-reduced sample not only has a larger high-temperature desorption peak area but also a shift in peak temperature towards higher temperatures, indicating that it has more active sites and a stronger hydrogen molecule adsorption capacity. Plasma hydrogen reduction not only completely removes oxygen from the catalyst precursor, but more importantly, its highly active hydrogen atoms and plasma bombardment can create more defects, vacancies, and other special structures on the material surface. These sites have a stronger adsorption effect on hydrogen, leading to higher temperatures for hydrogen desorption and an increase in the total adsorption amount. Therefore, compared to traditional molecular hydrogen reduction, plasma reduction can endow the catalyst with more and stronger hydrogen adsorption active sites, thus being more conducive to the ammonia synthesis reaction, and the plasma-reduced sample has higher activity.

[0059] To further verify the activity of the reduced samples under both conditions, in-situ electron paramagnetic resonance (EPR) technology was employed. This is a sensitive and direct method for detecting oxygen vacancies (V0, g around 2.003). The EPR spectra of the catalyst before and after the reaction are shown in Figure 5. The data show that at a g value of 2.0039, corresponding to V0, the EPR signal of the plasma-reduced zero-valent iron catalyst is stronger, indicating a higher V0 density. V0 enhances the catalyst's charge transfer ability, effectively promoting the transfer of electrons from the catalyst to N2 and H2 molecules, thereby increasing the NH3 concentration. The oxygen vacancy test further verifies that the plasma-reduced zero-valent iron has high activity.

[0060] Example 3 The main difference between this embodiment and Embodiment 1 is that, in the plasma ammonia synthesis reaction stage, the ammonia synthesis input power in this embodiment is 80W.

[0061] Example 4 The main difference between this embodiment and Embodiment 1 is that, in the plasma ammonia synthesis reaction stage, the ammonia synthesis input power in this embodiment is 100W.

[0062] The effects of different ammonia synthesis power levels were analyzed and compared, and the results are shown in Table 3. Table 3 shows that, with a fixed total reducing gas flow rate of 0.4 L / min, the ammonia concentration gradually increased with increasing input power. The lowest concentration was 10694 ppm at 80 W, while the concentration reached 13526 ppm when the power increased to 120 W. When the total reducing gas flow rate increased to 2 L / min, the ammonia concentration generally increased. This is mainly due to the increased content of highly active zero-valent iron with increasing total reducing gas flow rate, thus improving the ammonia concentration.

[0063] At a fixed reducing gas flow rate, increasing the input power enhances the electron density and energy of the plasma, generating more highly reactive hydrogen atoms, ions, and excited-state species. These active hydrogen species not only participate more effectively in the surface hydrogenation step but also help maintain the reduced state of active sites on the catalyst surface (such as zero-valent iron), thereby promoting nitrogen activation and ammonia synthesis reactions. Therefore, the concentration of synthesized ammonia increases with increasing power.

[0064] At a higher reducing gas flow rate (2 L / min), the higher power (120 W) further enhanced the efficient dissociation and activation of hydrogen by the plasma, and synergized with the increased zero-valent iron active sites to form a stronger "active hydrogen-active site" coupling, thereby obtaining the highest ammonia synthesis concentration under the conditions of 120 W and 2 L / min.

[0065] Table 3. Ammonia synthesis effect after plasma hydrogen reduction

[0066] Example 5 The main difference between this embodiment and Embodiment 1 is that the total flow rate of the H2 and Ar mixed gas during the plasma hydrogen reduction of iron stage in this embodiment is 1.5 L / min. The metallization rate and ammonia concentration during the plasma hydrogen reduction of iron stage in this embodiment are slightly lower than in Embodiment 1.

[0067] Example 6 The low-temperature plasma-coupled, highly active, low-cost zero-valent iron ammonia synthesis process of this embodiment includes: Step 1: Plasma hydrogen reduction of iron stage; 20g of high-purity Fe2O3 particles (with a particle size distribution of 1-3mm) were placed in a plasma reactor. A mixture of H2 and Ar gas (total gas flow rate of 1.0 L / min, H2:Ar volume ratio of 3:1) was introduced into the reactor, and a plasma hydrogen reduction reaction of iron was carried out at 400℃ to synthesize zero-valent iron. In this embodiment, the power input for the plasma hydrogen reduction stage was controlled at 90W, and the reduction time was 1.0 h. Simultaneously, a gas collection tank was used to recover the tail gas after plasma hydrogen reduction for subsequent ammonia synthesis.

[0068] Step 2: Plasma synthesis of ammonia reaction stage; After the plasma hydrogen reduction of iron reaction is completed, the zero-valent iron catalyst is kept in the reactor for ammonia synthesis. The H2 recovered in step one is used as a gaseous feedstock, and an appropriate amount of N2 is added. The H2 and N2 are mixed by introducing a gas mixing device, with the total flow rate of the H2 and N2 mixture set at 45 ml / min, and the H2:N2 volume ratio at 3:1. In the ammonia synthesis process, the plasma power input is controlled at 120 W, and the plasma reactor temperature is controlled at 220 °C. A liquid chromatograph is connected to the reactor tail end to detect the concentration of plasma-synthesized ammonia.

[0069] Example 7 The low-temperature plasma-coupled, highly active, low-cost zero-valent iron ammonia synthesis process of this embodiment includes: Step 1: Plasma hydrogen reduction of iron stage; 20g of high-purity Fe2O3 particles (with a particle size distribution of 1-3mm) were placed in a plasma reactor. A mixture of H2 and Ar gas (total gas flow rate of 1.5L / min, H2:Ar volume ratio of 4:1) was introduced into the reactor, and a plasma hydrogen reduction reaction of iron was carried out at 450℃ to synthesize zero-valent iron. In this embodiment, the power input for the plasma hydrogen reduction stage was controlled at 90W, and the reduction time was 1.5 h. Simultaneously, a gas collection tank was used to recover the tail gas after plasma hydrogen reduction for subsequent ammonia synthesis.

[0070] Step 2: Plasma synthesis of ammonia reaction stage; After the plasma hydrogen reduction of iron reaction is completed, the zero-valent iron catalyst is kept in the reactor for ammonia synthesis. The H2 recovered in step one is used as a gaseous feedstock, and an appropriate amount of N2 is added. The H2 and N2 are mixed by passing them through a gas mixing device, with the total flow rate of the H2 and N2 mixture set at 50 ml / min, and the H2:N2 volume ratio at 3:1. In the ammonia synthesis process, the plasma power input is controlled at 120 W, and the plasma reactor temperature is controlled at 250 °C. A liquid chromatograph is connected to the reactor tail end to detect the concentration of plasma-synthesized ammonia.

[0071] Example 8 The low-temperature plasma-coupled, highly active, low-cost zero-valent iron ammonia synthesis process of this embodiment includes: Step 1: Plasma hydrogen reduction of iron stage; 20g of high-purity Fe2O3 particles (with a particle size distribution of 0.1-1mm) were placed in a plasma reactor. A mixture of H2 and Ar gas (total gas flow rate of 1.8L / min, H2:Ar volume ratio of 5:1) was introduced into the reactor, and a plasma hydrogen reduction reaction of iron was carried out at 480℃ to synthesize zero-valent iron. In this embodiment, the power input for the plasma hydrogen reduction stage was controlled at 90W, and the reduction time was 100min. Simultaneously, a gas collection tank was used to recover the tail gas after plasma hydrogen reduction for subsequent ammonia synthesis.

[0072] Step 2: Plasma synthesis of ammonia reaction stage; After the plasma hydrogen reduction of iron reaction is completed, the zero-valent iron catalyst is kept in the reactor for ammonia synthesis. The H2 recovered in step one is used as the gaseous feedstock, and an appropriate amount of N2 is added. The H2 and N2 are mixed by passing them through a gas mixing device, with the total flow rate of the H2 and N2 mixture set at 55 ml / min, and the H2:N2 volume ratio at 3:1. In the ammonia synthesis process, the plasma power input is controlled at 120 W, and the plasma reactor temperature is controlled at 280 °C. A liquid chromatograph is connected to the reactor tail end to detect the concentration of plasma-synthesized ammonia.

[0073] Step 3: Measures to prevent sample oxidation after reduction; After ammonia synthesis is complete, Ar is introduced into the reactor as a protective gas, and the reactor temperature is allowed to drop to 50°C. o After the temperature drops below a certain point, turn off Ar and introduce an Ar-O2 mixture (97% Ar, 3% O2) into the reactor for 2 hours. Set the total flow rate to 250 ml / min. -1 At this point, a protective layer forms on the surface of the reduced sample, which effectively prevents the sample from being oxidized by air and does not affect the metallization rate or performance of the sample.

[0074] Example 9 The low-temperature plasma-coupled, highly active, low-cost zero-valent iron ammonia synthesis process of this embodiment includes: Step 1: Plasma hydrogen reduction of iron stage; 20g of high-purity Fe2O3 particles (with a particle size distribution of 1-3mm) were placed in a plasma reactor. A mixture of H2 and Ar gas (total gas flow rate of 2.0 L / min, H2:Ar volume ratio of 6:1) was introduced into the reactor, and a plasma hydrogen reduction reaction of iron was carried out at 500℃ to synthesize zero-valent iron. In this embodiment, the power input for the plasma hydrogen reduction stage was controlled at 90W, and the reduction time was 2.0 h. Simultaneously, a gas collection tank was used to recover the tail gas after plasma hydrogen reduction for subsequent ammonia synthesis.

[0075] Step 2: Plasma synthesis of ammonia reaction stage; After the plasma hydrogen reduction of iron reaction is completed, the zero-valent iron catalyst is kept in the reactor for ammonia synthesis. The H2 recovered in step one is used as a gaseous feedstock, and an appropriate amount of N2 is added. The H2 and N2 are mixed by passing them through a gas mixing device, with the total flow rate of the H2 and N2 mixture set at 60 ml / min, and the H2:N2 volume ratio at 3:1. In the ammonia synthesis process, the plasma power input is controlled at 120 W, and the plasma reactor temperature is controlled at 300 °C. A liquid chromatograph is connected to the reactor tail end to detect the concentration of plasma-synthesized ammonia.

[0076] Step 3: Measures to prevent sample oxidation after reduction; After ammonia synthesis is complete, Ar is introduced into the reactor as a protective gas, and the reactor temperature is allowed to drop to 50°C. o After the temperature drops below a certain point, turn off the Ar gas and introduce an Ar-O2 mixture (96% Ar and 4% O2) into the reactor for 1.8 hours at a total flow rate of 220 ml / min. -1 At this point, a protective layer forms on the surface of the reduced sample, which effectively prevents the sample from being oxidized by air and does not affect the metallization rate or performance of the sample.

Claims

1. A low-temperature plasma-coupled, highly active, low-cost process for synthesizing ammonia from zero-valent iron, characterized in that, include: A plasma reactor was used with hydrogen as a reducing agent to induce a plasma hydrogen reduction reaction in the Fe2O3 source in order to synthesize zero-valent iron. Using the zero-valent iron synthesized above as a catalyst, H2 and N2 are subjected to a plasma synthesis reaction to prepare ammonia; wherein, the plasma synthesis reaction is carried out under normal pressure and the reaction temperature is 220~300℃.

2. The low-temperature plasma-coupled, highly active, low-cost zero-valent iron ammonia synthesis process according to claim 1, characterized in that, The plasma hydrogen reduction reaction and the plasma ammonia synthesis reaction are carried out in the same plasma reactor, and the plasma input power is controlled to be 80~120 W.

3. The low-temperature plasma-coupled, highly active, low-cost zero-valent iron ammonia synthesis process according to claim 2, characterized in that, Also includes: Hydrogen gas is recovered from the plasma hydrogen reduction reaction and used as a raw material for the plasma ammonia synthesis reaction. After the plasma ammonia synthesis reaction is completed, the zero-valent iron sample is subjected to low-oxygen treatment using a mixture of inert gas and oxygen, wherein the mass percentage of oxygen in the mixture is 1% to 4%.

4. The low-temperature plasma-coupled high-activity, low-cost zero-valent iron ammonia synthesis process according to claim 2, characterized in that, After the plasma hydrogen reduction reaction is completed, the synthesized zero-valent iron is kept in the plasma reactor, and the temperature inside the reactor is reduced to the plasma ammonia synthesis reaction temperature range, so that it can continue to be used for plasma ammonia synthesis reaction.

5. The low-temperature plasma-coupled, high-activity, low-cost zero-valent iron ammonia synthesis process according to any one of claims 1-4, characterized in that, The Fe2O3 source is iron ore with a particle size of 0.1~3mm.

6. The low-temperature plasma-coupled, highly active, low-cost zero-valent iron ammonia synthesis process according to claim 5, characterized in that, The iron ore has a particle size of 1-3 mm.

7. The low-temperature plasma-coupled, high-activity, low-cost zero-valent iron ammonia synthesis process according to any one of claims 1-4, characterized in that, The plasma hydrogen reduction reaction is carried out at a temperature of 400-500℃ and for a time of 1-2 hours.

8. The low-temperature plasma-coupled, highly active, low-cost zero-valent iron ammonia synthesis process according to claim 7, characterized in that, The discharge section of the plasma reactor is heated by a furnace to regulate the temperature inside the reactor.

9. The low-temperature plasma-coupled, high-activity, low-cost zero-valent iron ammonia synthesis process according to any one of claims 1-4, characterized in that, During the plasma hydrogen reduction reaction, a mixture of hydrogen and argon is introduced into the reaction system. The total flow rate of the mixture is 1-2 L / min, and the volume ratio of H2 to Ar is 3:1-6:

1.

10. The low-temperature plasma-coupled, high-activity, low-cost zero-valent iron ammonia synthesis process according to any one of claims 1-4, characterized in that, The total flow rate of the H2 and N2 mixture in the plasma ammonia synthesis reaction is 45~60 ml / min, and the volume ratio of H2:N2 is 3:1.

Images